You may have noticed that things look a little different. SimpleMDM is now part of the PDQ.com family and we are in the process of moving all of the SimpleMDM Knowledge Base articles to their new home. If you notice any links that are broken or if anything does not work as expected, please email email@example.com and let us know!
The following articles from Apple's support documentation provide a list of network requirements / ports used by Apple services:
Requests from SimpleMDM come from "a.simplemdm.com".